2'-O-methyl-5-formylcytidine (f5Cm), a new modified nucleotide at the 'wobble' of two cytoplasmic tRNAs Leu (NAA) from bovine liver

Abstract

The nucleotide analysis of a cytoplasmic tRNA ^Leu isolated from bovine liver revealed the presence of an unknown modified nucleotide N. The corresponding N nucleoside was isolated by different enzymatic and chromatographic protocols from a partially purified preparation of this tRNA ^Leu . Its chemical characterization was determined from its chromatographic properties, UV-absorption spectroscopy and mass spectrometric measurements, as well as from those of the borohydride reduced N nucleoside and its etheno-trimethylsilyl derivative. The structure of N was established as 2′- 0 -methyl-5-formylcytidine (f ⁵ Cm), and its reduced derivative as 2′- 0 -methyl-5-hydroxy-methylcytidine (om ⁵ Cm). By sequencing the bovine liver tRNA ^Leu , the structure of the anticodon was determined as f ⁵ CmAA. In addition, the nucleotide sequence showed two primary structures differing only by the nucleotide 47c which is either uridine or adeno-sine. The two slightly differing bovine liver tRNAs- ^Leu (f ⁵ CmAA) are the only tRNAs so far sequenced which contain f ⁵ Cm. The role of such a modified cytidine at the first position of the anticodon is discussed in terms of decoding properties for the UUG and UUA leucine codons. Recently, precise evidence was obtained for the presence of f ⁵ Cm at the same position in tRNAs ^Leu (NAA) isolated from rabbit and lamb liver. Therefore, the 2′- O -methyl-5-formyl modification of cytidine at position 34 could be a general feature of cytoplasmic tRNAs ^Leu (NAA) in mammals.